Follow the standard nodename pattern "^nand-controller(@.*)?" defined
in Documentation/devicetree/bindings/mtd/nand-controller.yaml

Otherwise, after the dt-binding is converted to json-schema,
'make ARCH=arm dtbs_check' will show warnings like this:

  nand@68000000: $nodename:0: 'nand@68000000' does not match '^nand-controller(@.*)?'
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>